Known insulated pipelines for such transports are constructed and formed so that they can be placed below or above ground and have also appeared to be directly unsuitable for use under water at great depths for transport of oil and gas from oil fields at sea. A pipeline that is to be placed under water and at great depths, for example 300-400 m, will be subjected to great hydrostatic pressures that known pipelines do not manage without collapsing and, moreover, it is necessary that subsea pipelines have not only a good heat insulation but also protection against mechanical damage and water penetration in order to prevent corrosion, not the least considering the difficulties in repairing such pipe lines disposed at great depths.
Laying out subsea pipelines also requires another technology than that normally used for pipelines to be placed below or above ground, and this can be carried out from great drums having a diameter of about 18 m on which the pipeline is wound up. Due to this laying technique the insulating and protective layers of the pipeline will also be exposed to great bending stresses which known protective and insulating layers for pipelines of this type often do not manage.
For pipelines intended to be placed on the bottom of the sea an outer protective layer in the form of steel mantles with watertight partitions has been used, but this type of protective layer is not satisfactorily corrosion-resistant and not suitable for coiling on laying-out drums, either.